The semiconductor integrated circuit industry has experienced rapid growth in the past several decades. Technological advances in semiconductor materials and design have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. In the course of semiconductor evolution, the number of interconnected devices per unit of area has increased as the size of the smallest component that can be reliably created has decreased.
Many of the technological advances in semiconductors have occurred in the field of memory devices, and some of these involve capacitive structures. Such capacitive structures include, for example, metal-insulator-metal (MIM) capacitors. In particular, resistive random access memory (RRAM) is one technology for non-volatile memory devices built on MIM capacitor structures. In an RRAM device, each RRAM cell (MIM cap) includes a resistive material layer, the resistance of which can be adjusted to represent a logic value by switching the device between a low resistance and high resistance state.
One typical operation of an RRAM cell involves making the resistive material layer a conductor through formation of a conductive filament (conduction path) by applying of a sufficiently high electric field. Once the filament is formed, it may be reset (broken, resulting in high resistance) or set (re-formed, resulting in lower resistance). In one example, the conduction through the MIM stack and the conductive filament is by defects in the resistive material layer, known as oxygen vacancies (oxide bond locations where the oxygen has been removed), which can subsequently charge and drift under an electric field. In other words, the conductive filament forms an oxygen vacancy bridge through the MIM cap stack. Resetting the RRAM to a high resistance state provides for the recombination of the oxygen ions with the oxygen vacancies thereby disrupting the bridge.
One advantage of these and other MIM cap devices is their compatibility with CMOS fabrication processes. Current fabrication methods and structures for using MIM caps as RRAM devices, including those implicating the formation and preservation of the filament, while suitable in many respects, can struggle to meet the desired performance and reliability criteria.
The various features disclosed in the drawings briefly described above will become more apparent to one of skill in the art upon reading the detailed description below. Where features depicted in the various figures are common between two or more figures, the same identifying numerals have been used for clarity of description.